In order to allow a semiconductor device to be high in breakdown voltage and low in loss and to be used in a high-temperature environment, silicon carbide has recently increasingly been adopted as a material forming a semiconductor device. Silicon carbide is a wide band gap semiconductor greater in band gap than silicon which has conventionally widely been used as a material forming a semiconductor device. Therefore, by adopting silicon carbide as a material forming a semiconductor device, a higher breakdown voltage and a lower on-resistance of a semiconductor device can be achieved. A semiconductor device in which silicon carbide has been adopted as a material is also advantageous in that lowering in characteristics during use in a high-temperature environment is less than in a semiconductor device in which silicon has been adopted as a material.
For example, Japanese Patent Laying-Open No. 2008-147232 (PTD 1) describes a trench metal oxide semiconductor field effect transistor (MOSFET) composed of silicon carbide. According to the MOSFET, a thickness of a channel layer is set to at least a thickness calculated in a prescribed calculation formula so as not to cause punch through due to a short channel effect, and a lower end of a base layer is provided on a side of a drain electrode relative to a lower end of a gate trench.
Y. Nakano et al., “690V, 1.00 mΩcm2 4H-SiC Double-Trench MOSFETs,” Materials Science Forum Vols. 717-720 (2012) page 1069-1072 (NPD 1) describes a MOSFET in which a trench for holding a breakdown voltage is fabricated adjacently to a trench for switching and a bottom portion of the trench for holding a breakdown voltage is provided on a side of a drain electrode relative to a bottom portion of the trench for switching. A p-type base layer is provided under the trench for holding a breakdown voltage.